1. Field of the Invention
The present invention relates generally to an active suspension control system for a vehicle for suppressing vehicular rolling motion caused by lateral acceleration acting on a vehicle body. More particularly, the invention relates to an active suspension control system for adjusting wheel loads acting on driven wheels according to a wheel speed difference between the driven wheels to secure acceleration characteristics and driving stability, for example, when a vehicle travels on a road surface having different friction coefficients between left and right wheels.
2. Description of the Background Art
Japanese Patent First Publication No. 2-3511 which corresponds to the U.S. Pat. No. 5,114,177, discloses an active suspension control system. This control system determines whether a friction coefficient of a road surface on which a vehicle travels is smaller than that of a standard road or not. If the result indicates that the vehicle travels on a lower friction road surface, active suspension control is effected so that anti-rolling moment for rear wheels is provided smaller than that for front wheels, for shifting a load acting on the rear wheels to less than that acting on the front wheels, allowing a rear portion of a vehicle body to roll slightly to secure the cornering abilities of the rear wheels for improving driving stability on the lower friction road surface. Determining the friction coefficient of the road surface is accomplished by utilizing either of a lateral acceleration acting on the vehicle body or a wheel speed difference between driven and compliance wheels. A ratio of the rear anti-rolling moment to the front anti-rolling moment is varied based on a value of the lateral acceleration or the wheel speed difference. Accordingly, this prior art active suspension control system establishes improved cornering characteristics when lateral acceleration acts on the vehicle body. However, the above mentioned system does not serve to secure desired acceleration characteristics and driving stability when the vehicle travels on a road surface having different friction coefficients between left and right wheels.
Japanese Utility Model First Publication No. 62-191511 discloses an active suspension control system which is directed to increase a wheel load acting on a skidding driven wheel according to a wheel speed difference between left and right driven wheels only, irrespective of lateral acceleration acting on a vehicle body. Accordingly, this prior art suspension control system has disadvantages in that a variation in a wheel load caused by suspension control when a vehicle travels on a lower friction road surface is the same as that when traveling on a higher friction road surface even if lateral accelerations are different between the lower friction and the higher friction road surfaces. Thus, traction of the driven wheels is not secured effectively.